\tracingonline=2
\tracingcommands=2
\tracingmacros=2
\tracingrestores=2

\catcode`{=1
\catcode`}=2

{

\hbox{ abc def }
\hbox  \relax  \relax { abc def }
\hbox to 2pt \relax { abd def }
\hbox spread 2pt \relax { abd def }

\vbox{ abc def }
\vbox  \relax  \relax { abc def }
\vbox to 2pt \relax { abd def }
\vbox spread 2pt \relax { abd def }

\vtop{ abc def }
\vtop  \relax  \relax { abc def }
\vtop to 2pt \relax { abd def }
\vtop spread 2pt \relax { abd def }

\box0
\box1
\box-1
\box277

\copy0
\copy-1

\vsplit2to4pt
\vsplit-1to3pt
\vsplit2 4pt
\vsplit to 4pt

\setbox0=\hbox to 10pt{abc}
\setbox1=\hbox spread 11pt{abc}
\setbox2=\vbox to 12pt{abc}
\setbox3=\vbox spread 13pt{abc}
\setbox4=\vtop to 14pt{abc}
\setbox5=\vtop spread 15pt{abc}
{
    \setbox0=\hbox{a}
    \setbox1=\hbox{a}
    \setbox2=\hbox{a}
    \setbox3=\hbox{a}
    \setbox4=\hbox{a}
    \setbox5=\hbox{a}
}

\lastbox

\hbox abc }
\vbox abc }
\vtop abc }

\setbox2=\hbox{ abc def }
\setbox2=\hbox  \relax  \relax { abc def }
\setbox2=\hbox to 2pt \relax { abd def }
\setbox2=\hbox spread 2pt \relax { abd def }

\setbox2=
\setbox2=\vbox{ abc def }
\setbox2=\vbox  \relax  \relax { abc def }
\setbox2=\vbox to 2pt \relax { abd def }
\setbox2=\vbox spread 2pt \relax { abd def }
\setbox2=
\setbox2=\vtop{ abc def }
\setbox2=\vtop  \relax  \relax { abc def }
\setbox2=\vtop to 2pt \relax { abd def }
\setbox2=\vtop spread 2pt \relax { abd def }
\setbox2=
\setbox2=\box0
\setbox2=\box1
\setbox2=\box-1
\setbox2=\box277
\setbox2=
\setbox2=\copy0
\setbox2=\copy-1
\setbox2=
\setbox2=\vsplit2to4pt
\setbox2=\vsplit-1to3pt
\setbox2=\vsplit2 4pt
\setbox2=\vsplit to 4pt
\setbox2=
a\setbox2=\lastbox
\setbox2=
\setbox2=\hbox abc }
\setbox2=\vbox abc }
\setbox2=\vtop abc }

}

\end
